In a noisy city or factory site, a double-window installation comprised of two windows respectively slidingly mounted on two tracks or a window comprised of two layers of glass sheets may be provided to reduce noise pollution and prevent hearing loss for the people living in a building or house located in the noisy surroundings. However, such a window still has the following defects:
1. There is an air chamber still existing in between the two windows or two glass sheets, being able to transmit sound wave through the air medium to thereby reduce its efficiency for shielding noise.
2. For the double-window installation, there is a great aperture between the windows and the rails or tracks to possibly transmit sound wave into the interior of a building to reduce the noise-prevention efficiency.
3. If for burglar prevention purpose, an ironic bar grating should be further installed outside the window for security reason, which however looks like a barred window as found in a prison, resulting in a very bad appearance of a building and also obstructing the escape action in case of a fire.
The present inventor has found the defects of a conventional window installation for shielding noise, and invented the present door and window apparatus having dual purpose of noise and burglar prevention.